If a motor vehicle needs to have power brakes and uses vacuum-assisted brakes, it must have a well-maintained vacuum gauge that is accurate within 10% and easily readable by the driver. However, this rule doesn't apply to two-axle trucks driving alone.

This law requires vehicles with power brakes, specifically those using vacuum or vacuum-assisted brakes, to have a warning signal, either sound or light, to alert the driver when the vacuum pressure is too low (eight inches of mercury or less). A vacuum gauge alone is not enough to satisfy this requirement. However, this rule does not apply to two-axle trucks driven solo or vehicles made before 1964.

If a vehicle must have power brakes that use vacuum or vacuum-assisted systems, it needs to have a check valve installed and kept in good condition. This check valve should be placed in the vacuum system between where the vacuum is created and the vacuum reserve.